1. Field of the Invention
This invention relates to a method and material employed for recovery of palladium and gold from base metals and impurities. More particularly it relates to a system and method employing a single novel extractant in a method allowing for extraction of palladium and gold from acidic media containing chloride ions.
2. Prior Art
Throughout the world, for centuries, their has been a continuing demand for precious metals. In earlier times such was desirable for decorative purposes and as a means to store wealth of regents. More modernly, in addition to decorative purposes, precious metals are employed throughout the world in products such as electronics. With the ongoing metamorphosis of countries like China into high technology manufacturers and consumers, there continues to be an ever increasing industrial demand for precious metals. The increasing industrial use, and increased ownership by individuals and governments during current economic times, has driven the price for precious metals to historic highs.
Mining of precious metals has become prohibitively costly and the minerals extracted by mining is unable to keep up with the logarithmic increase in demand. The above noted increased ownership and use, and the lessening supply from mined sources of precious metals, and the resulting high prices for such metals, has made the processes of recovering and refining these metals from other underused sources, potentially a very significant source, if they can be extracted and delivered at reasonable prices through refining and extracting of underutilized sources already existing.
Copper anode slime is one of the major sources of the precious metals. Copper anode slime occurs in copious quantities during copper smelting. The anode slime collects at the bottom of conventional electrolytic copper refining cells. This anode slime contains significant quantities of platinum group metals especially platinum and palladium. The slime also contains significant quantities of gold, silver, aluminum, zinc, copper, arsenic, selenium, tellurium, nickel, and iron.
Smelting firms are cognizant of the slime contents and conventionally employ a solvent extraction process to the anode slime to achieve a concentration, separation, and final extraction of precious metals by these large industrial companies. Despite simplicity and other advantages of solvent extraction process in precious metals recovery from copper anode slime, serious problems associated with the process exist which must be solved.
Major impediments to the reagent used in such solvent extraction processes of precious metals exist in the recovery procedure, including extraction and stripping rate, extractant consumption, and selectivity. Two conventional extractants employed in this process include Dibutyl carbitol (DBC) and di-n-hexyl sulfide (DHS). These are employed as preferred extractants to yield gold and palladium respectively in the extraction process from sources such as copper anode slime. Prior art has sought to solve some of these problems without significant success.
U.S. Pat. No. 7,291,202 describes the extraction of 1 mol gold from PGM concentrate by employing about 75 mol DBC. The extraction time using this quantity of DBC is taught at about 10 minutes. As taught in this patent, the extraction of gold with DBC from the subject material required five different stages. The process employed 2 stages for initial extraction, and three stages of scrubbing are then employed using 5 M hydrochloric acid solutions. This method involves problems, one of which is the large amount of extractant DBC used for extraction of gold for the ten minute time duration. Further, the taught method requires multi-steps for both extraction and for scrubbing stages. It is thus time consuming and expensive due to the amount of labor and extractant material that is used. Further, the conventional palladium extractant (DHS) taught for use for extraction of palladium to yield a molar ratio of 6:1 (DHS:Pd) requires no less than 3 hours of time. The '202 patent describes that gold disturbs the extraction of palladium with DHS. Thus for extraction of palladium by DHS, gold must be removed at first because DHS cannot extract gold and/or palladium simultaneously. Consequently, there is a major drawback of DHS employed as an extractant since it yields a very low extraction kinetic and is time consuming.
U.S. Pat. No. 5,284,633 teaches a new technique for separating of gold, palladium and platinum from the available material such as anode slime. This patent teaches the use of a single extractant, kelex 100, to be employed as the extraction reagent. However the '633 patent has some serious flaws also.
First, using the method and extractant of the '633 patent, yields a low extraction of precious metals using a feed solution which is employed in a high volume. The extractant consumption for recovery of precious metals from the taught feed solution used of substantially 200 mol of kelex 100 yields only 1 mol of recovered precious metal. Using this 200:1 ratio, the extraction time takes at least 2 minutes. Further, because the employment of kekex 100 also extracts iron to the organic phase at a taught ratio of 27%, it requires scrubbing and the scrubbing process in each stage eliminates a portion of the precious metals which are being recovered, from the organic phase (Au: 3%, Pt: 6% and Pd: 2%) thereby increasing cost from lower yields.
U.S. Pat. No. 7,597,863 teaches the utilization of sulfur containing diamide agents for the extraction of palladium. In the '863 patent, it is taught that 200 mol the extractant must be employed to yield a recovery of 1 mol palladium. Using this costly 200:1 ratio is especially time consuming as it lasts at least 10 minutes. The '863 thus has some major disadvantages since it requires a very high consumption of the extractant for the low yield, and it uses a hydrochloric acid solution containing thiourea in the eventual stripping stage which is conventionally not considered suitable for practical widespread application. Due to some shortages of the ingredients of this and other above noted extractants, costs are increased and production slowed.
As such, there exists an unmet need for a more effective and economical system employing a more practical reagent in the extraction of precious metals from sources such as copper anode slime and the like. Such a method should yield the highest amount of recovered precious metal with a significantly lower utilization of extractant than current systems. Finally, thus a system and extractant should significantly reduce the time needed for the process by the elimination of time-consuming scrubbing stages so that production may speed up and further lower costs by increasing valuable recovered precious metals using less labor and extractant material.